Large composite structures may be fabricated using automated, composite tape layup machines (CTLMs). These relatively large and expensive machines use a computer controlled tape placement head to simultaneously lay down multiple strips of composite prepreg tape on a mandrel or other surface. The head places the tape strips in substantially parallel relationship and in edge-to-edge contact, however, small gaps may occur between edges of adjacent strips. If these gaps exceed an allowable tolerance, they may affect the quality and/or performance of the completed structure. When gaps exceed the allowed tolerance, it may be necessary to rework these areas of the structure in order to bring the structure to within manufacturing specifications. Following rework of the tape strips, the areas are re-inspected to assure that tape gaps have been brought to within specified tolerances.
Currently, the tape gap inspection process may be performed by a technician using a hand gauge to make each individual tape gap measurement. The technician is required to manually reposition the gauge to each measurement point along the length of a reworked tape. At each measurement point, the technician kneels and takes a visual gap reading. This hand measurement technique is labor intensive and may be impractical for use on large scale structures because of the number of measurements that may be necessary and the time required to complete the measurements. Also, the accuracy of the hand held measurements may be subject to the skill level of the technician.
Tape gaps may also be measured automatically a using non-contact inspection device integrated into the tape placement head of the CTML, however this solution may require that the CTML be taken off-line from production to perform the inspection process. The resulting machine downtime may reduce production throughput, and may be inefficient where only a single reworked tape strip requires inspection.
Accordingly, there is a need for a method and apparatus for measuring tape gaps that is accurate and efficient in carrying out multiple tape gap measurements over large areas of a structure, and which is not highly dependent upon operator skill.